We have shown that schizophrenic patients show higher growth hormone responses to apomorphine hydrochloride than do normals but only on certain occasions when studied longitudinally. Growth hormone responses tend to be exaggerated at the time of relapse, and during remission may be blunted or exaggerated. Only patients who at some time demonstrate incoherent thinking and formed delusions have exaggerated growth hormone responses. Resting serum prolactin varies in some patients much more than in normal controls and tends to decline to very low levels at the time of relapse. Several possible sources of variance remain to be controlled. However, it is tempting to infer that the instability of growth hormone responses and resting prolactin levels may signify instability in the regulation of these hormones by dopamine. The present proposal describes an attempt to replicate these findings on a new sample of schizophrenci patient on drug holiday. The test procedure has been simplified for the sake of effeciency and with a view to developing a practical test. Several sources of possible variance will be monitored. An experiment to examine a possible placebo response to saline is also proposed.